How many half life games are there?
Half-Life, Half-Life: Blueshift, Half-life: Opposing Force,
Half-life: High Definition pack (might not classify as a game),
Half-Life: Source, Half-Life 2, Half-Life 2: Episode 1, and
Half-Life 2: Episode 2. Eight games total not including countless
mods created by fans that you can download for free on moddb.com
and fileplanet.com. Other games by Valve software include Left 4
Dead, Left 4 Dead 2, Portal, Portal 2, Counter Strike, Counter
Strike: Source, Team Fortress, Team Fortress 2, and Alien
Swarm.
Another Half-Life game would be Half-Life: Decay. You might also
be able to count Half-Life Deathmatch and Half-Life 2
Deathmatch.